Direct positive photographic materials



United States Patent Ofiice 3,284,203 Patented Nov. 8, 1966 This application is a continuation-in-part of application Serial Number 189,984, filed April 25, 1962 now abandoned.

The instant invention relates to silver halide direct positive photographic materials. It is well known that fog centers created in a photographic silver halide emulsion, either by adding chemical agents such as hydroxylamine or by exposing the emulsion to blue light, can be at least partly destroyed by exposing the same .to long-wavelength radiation before it is developed by a conventional manner. Such a phenomenon is known as the Herschel eifect and the present invention is one which utilizes this phenomenon to obtain a direct positive image.

Direct positive photographic materials have a low photographic senstivity requiring a light source of high luminance, for example, a mercury lamp, for printing. The low photosensitivities of these mate-rials also have the advantage of being safely handled under a relatively bright room illumination; that is, they can be handled without difficulty under normal room illumination of, for example, a 100 w. tungsten lamp at a distance of 1 m. for up to 8 minutes. When the materials are exposed to the light of a tungsten lamp for a longer time, the density of area which ought to be darkened after exposure and development tends to decrease. Moreover, when such materials are exposed under a bright light, a comparatively short time exposure gives grey or black fog area where it ought to be white or transparent. Modern ofiices favor the use of such artificial lights as fluorescent lamps, mercury lamps, flood lamps and natural daylight. The handling of direct positive photographic materials known heretofore under such illumination causes an undesirable tendency to induce fogging.

. The primary object of this invention is to provide direct positive photographic materials that can be safely handled under such illumination. More precisely, with the materials of this emulsion, even though they are handled in a bright light illumination they give no grey or black area where it ought to be White or transparent in the finished prints or films.

We discover that the wavelengths of light tending to cause such fog are related to the spectral sensitivity of silver halide contained in the direct positive photographic materials. In other words, the fog appears in the finished printing paper and the film after exposure and development, when the direct positive photographic materials are exposed to light of Wavelengths below 450 my. in the case of pure silver chloride as photosensitive material; below 470 run in the case of silver chloride-bromide, and below 500 mp. in the case of silver bromide.

It some substances which absorbs part or all of the light of the wavelength to which the direct positive photographic emulsion is sensitive is added to the emulsion, or a gelatin layer containing such substance is coated on the emulsion, the finished material does not have a tendency to fog even when it is exposed to bright illumination from a fluorescent lamp or from daylight. Our study concluded that the ultraviolet absorbing dyes are effective to a nearly satisfactory extend as the said substance.

Other materials serving for this purpose include 3-nitrophthalic acid, l-sulfioan-thnaquinone, Z-sulfoanthraquinone, sodium sulfonate of 2-anilinonaphthalene, l-oxy-Z-naphthoic acid, Z-hydroxynaphthalene-l, S-disulfonic acid, 2- hydroxy-4-methoxybenzophenone-5-sulfonic acid, and sodium 4,4'-bis (dimethylamino) benzophenone-Isfi'-disulfonate.

The following will serve to illustrate the manner whereby the ultraviolet abs-orbents other than known organic compounds are synthesized.

The sodium sulfonate of 2-anilinonaphthalene (or sodium 2anilinonaphthalene-x-sulfonate wherein x represents a sulfone group but its substitution position is not clear) represented by the formula is obtained by heating :a mixture of 1 part of Z-anilinonaphthalene and 4 parts of concentrated sulfuric acid at C. to be sulfonated and salting-out.

The aqueous solution has A of 380 mp and a MP. of more than 300 C.

The 2-hydroxy-4-methoxybenzophenone-5-su1fonic acid represented by the formula is obtained by heating a mixture of 1 part of Z-hydroxy- 4-methoxybenzophenone and 4 parts of 5% fuming sulfuric acid at about 80 C. to be sulfion-ated. The mixture is then introduced into 10 parts of iced water and neutralized with calcium hydroxide, the precipitate of calcium sulfate being filtered off. A small amount of sulfuric acid is added to the filtrate until the precipitation of calcium sulfate is no longer effected, the pH of the filtrate being then about 4. A small quantity of calcium sulfate is :refiltered and the filtrate is condensed.

The aqueous solution has A of 350 mp. and a MP. of over 300 C.

The sodium-4,4-bis (dimethylamino) 'benzophenone- 3,3-disulfonate represented by the formula SO Na SO Na OCHs is obtained by heating, under stirring, a mixture of l part of Michlers ketone and 6 parts of 40% fuming sulfuric acid at to C. until a sampling of the heated mixture is completely dissolved in ammonia water, and salting-out with common salt water.

The aqueous solution has A of 370 III/.0 and 2. MP. of over 300 C.

The following examples illustrate the invention more fully.

Example I One kg. of silver chloride emulsion was ripened at 50 C. for about 40 minutes and washed with Water. Before ripening, 15 cc. of 2% sodium carbonate were added to adjust the pH value to about 8.0, and also 15 cc. of 1% hydroxylamine were added. After completion of ripening, 13 cc. of 1% aqueous sulfuric acid was added to make the pH value about 6.0. Then, before coating, to 1 kg. of the emulsion were added 60 cc. of 0.1% Pinacryptol Green (desensitizing dye), 15 cc. of 5% chrome alum, 10 cc. of 5% Saponin and 20 cc. of 1% l-sulfoanthraquinone. The thus prepared emulsion was coated on a photographic paper (about 85 gms./m. A control emulsion was also prepared which was the same as the above except that the l-sulfoanthraquinone was not used and it was coated on similar photographic paper. After drying, these two kinds of photographic paper were exposed to two 40 W. fluorescent lamps of daylight type at a distance 1 m. with the emulsion surfaces toward the light source, for varying time durations of 1, 3, 5, 10 and 20 minutes. Then the t-hus exposed paper was further exposed to light from a 1 kw. mercury lamp for 10 seconds at a distance of 10 cm. through a yellow filter (Kodagraph sheeting yellow). These pieces of paper were then developed in the Kodak D72 developer (diluted with two parts of water) having the following composition G. Monomethylparamino phenol sulfate 3.0 Sodium sulfite 45.0 Hydroquinone 12.0 Sodium carbonate (mono-hydrated) 80.0 Potassium bromide 2.0

Water to make 1.0 liter.

at 20 C. for 60 seconds. The density of the fogs resulting from being exposed to the fluorescent light are shown in the following table.

TABLE Duration of Exposure (min) 1 3 5 Control 0.0 0.2 0.7 1. 0 1.1 1.1 l sulloanthraquiuonc added 0. 0 0.0 0.0 0.3 0. 4 0v 6 It is evident from the above table that adding of 1- sulfoanthraquinone to the emulsion reduced the appearance of fog used by the fluorescent light.

Example II A control emulsion as described in Example I was coated on a photographic paper (about 85 gms./m. allowed toset and over-coated with a gelatin solution having the following formula:

Gelatin gms 20 Water mls 1000 1% 2 hydroxy-4-methoxybenzophenone-S-sulfonic acid mls 20 Saponin 5% solution mls 10 Example III To an emulsion prepared as described in Example I without the l-sulfoanthraquinone, cc. of 1% sodium solution of 2-anilinonaphthalene were added.

The testing results were similar to those realized with the materials of Example I.

Example IV The procedure of Example I is followed using a solution of 0.8 g. of 3-nitrophthalic acid in 20 cc. of 1% sodium carbonate solution in place of 20 cc. of 1% 1- sulfoanthraquinone. Substantially the same results as those of Example I are obtained.

4 Example V The procedure of Example I, using 40 cc. of 0.5% 2- sulfoanthraquinone in place of 20 cc. of 1% l-sulfoanthraquinone is followed. Substantially the same results as those of Example I are again obtained.

Example VI The procedure of Example I is followed replacing the 1% l-sulfoanthraquinone with 40 cc. of 0.5% 1-oxy-2- naphthoic acid. Similar good results are obtained.

Example VII The procedure of Example I is followed using 20 cc. of 1% 2-hydroxynaphthalene-1,5-disulfonic acid in place of 20 cc. of 1% l-sulfoanthraquinone. Once again, the good results are realized.

Example VIII The procedure of Example I using 4 cc. of 5% sodium 4,4 bis (dimethylamino) -benzophenone-3,3'-disulfonate in place of the 20 cc. of 1% l-sulfoanthraquinone produces comparable results.

Example IX For illustration of direct positive photographic materials of this invention in Herschel effect development utilizing image.

Example X The direct positive material coated with the control emulsion and the direct positive material of this invention containing l-sulfoanthraquinons shown in Example I were printed from an original, such as, a drawing and a document through a yellow filter, Kodagraph sheeting yellow filter using a diazo printer placed in a bright room illuminated by fluorescent lamps. Thus printed both direct positive materials were developed at 20 C. for seconds in the developer D72 (diluted with two parts of water) and then subjected to fixing, rinsing and drying.

By such exposing and developing processes, the fogging nuclei pre-formed during the production of the emulsion are developed to give a blackened silver image on the pertions of the direct positive material corresponding to the pattern (black) portions of the original, but the fogging nuclei in the portions corresponding the blank portions of the original are broken by the Herschel effect caused by long-wave length light passed through the yellow filter to give blank portions there.

Now, on comparing the improved photosensitive material of this invention added with 1;-sulfoanthraquinone with the photosensitive material coated with the control emulsion in Example I, the former gave a good copy having no fog by such exposing and developing processes whereas the latter gave an only inferior copy since there formed fogs as shown in example in the portions to be reversed into white by the Herschel effect.

Thus, it will now be seen that there is herein provided an improved direct positive photographic material which satisfies all of the objectives of the instant invention, and others, including many advantages of great practical utility and commercial importance.

Since there are many embodiments of the instant inventive concept, and since there are many modifications of the embodiments hereinbefore shown and described, it is to be understood that all matter herein is to be interpreted merely as illustrative and not as limiting.

Accordingly, what is claimed is:

1. A direct positive photographic material comprising a layer of a silver halide emulsion having latent fog centers which are depressed by Herschel effect on exposure to a long-wavelength light and a surface layer adjacent to the emulsion layer, at least one of said layers containing a material selected from the group consisting of Z-hydroxy- 4-methoxybenzophenone-5-sulfonic acid and sodium 4,4- bis (dimethylamino) benzophenone-3,3'-disulfonate.

2. A direct positive photographic material com-prising a layer of a silver halide emulsion having latent fog centers which are depressed by Herschel eflect on exposure to a long-wavelength light and a surface layer adjacent to the emulsion layer, at least one of said layers containing 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid.

3. A direct positive photographic material comprising a layer of a silver halide emulsion having latent fog centers Which are depressed by Herschel elfect on exposure to'a long-Wavelength light and a surface layer adjacent to the emulsion layer, at least one of said layers containing sodium 4,4-bis (dimethylamino) benzophenone-3,3'-disulfonate.

References Cited by the Examiner FOREIGN PATENTS 1/ 1957 Germany. 6/1929 Great Britain.

I. TRAVIS BROWN, Acting Primary Examiner. 

1. A DIRECT POSITIVE PHOTOGRAPHIC MATERIAL COMPRISING A LAYER OF A SILVER HALIDE EMULSION HAVING LATENT FOG CENTERS WHICH ARE DEPRESSED BY HERSCHEL EFFECT ON EXPOSURE TO A LONG-WAVELENGTH LIGHT AND A SURFACE LAYER ADJACENT TO THE EMULSION LAYER, AT LEAST ONE OF SAID LAYERS CONTAINING A NATERUAK SELECTED FROM THE GROUP CONSISTING OF 2-HYDROXY4-METHOXYBENZOPHENONE-5-SULFONIC ACID AND SODIUM 4,4''BIS (DIMETHYLAMINO) BENZOPHENONE-3,3''-DISULFONATE. 